A systematic comparison of two empirical gas-liquid mass transfer determination methodologies to characterize methane...

This study aimed at systematically comparing the potential of two empirical methods for the estimation of the volumetric CH₄ mass transfer coefficient (k_la_CH4), namely gassing-out and oxygen transfer rate (OTR), to describe CH₄ biodegradation in a fermenter operated with a methanotrophic consortium at 400, 600 and 800 rpm. The k_la_CH4 estimated from the OTR methodology accurately predicted the CH₄ elimination capacity (EC) under CH₄ mass transfer limiting conditions regardless of the stirring rate (∼9% of average error between empirical and estimated ECs). Thus, empirical CH₄-ECs of 37.8 ± 5.8, 42.5 ± 5.4 and 62.3 ± 5.2 g CH₄ m^-3 h^-1vs predicted CH₄-ECs of 35.6 ± 2.2, 50.1 ± 2.3 and 59.6 ± 3.4 g CH₄ m^-3 h^-1 were recorded at 400, 600 and 800 rpm, respectively. The rapid Co²⁺-catalyzed reaction of O₂ with SO₃^-2 in the vicinity of the gas-liquid interphase during OTR determinations, mimicking microbial CH₄ uptake in the biotic experiments, was central to accurately describe the k_la_CH4.